Treatment of cellulose esters containing colloiding agents



Jan. 19, 1937. D. MCBURNEY T AL 2,057,938

TREATMENT OF CELLULOSE ESTERS CONTAINING COLLOIDING AGENTS Filed Oct. 4, 1934 Dorman M- fiume y, INVENTORS fdyar f7. lVo/lau BY 5 G2,

ATTORNEY.

Patented Jan. 19, 1937 STTES PATENT OFFNE TREATMENT OF CELLULOSE ESTERS CONTAINING COLLOIDING AGENTS Application October 4, 1934, Serial No. 746,782

7 Claims. (Cl. 260-133) This invention relates to a method of removing colloiding agents from cellulose esters, and more particularly, toa method of treating cellulose nitrate containing camphor to recover both the cellulose nitrate and camphor. This is a continuation-in-part of application Serial No. 556,506 filed August 12, 1931.

Scrap Celluloid, French ivory, photographic film base, and the like, furnish a cheap and plen- 10 tiful source of cellulose esters and of the various colloiding agents used in plasticizing cellulose esters. The use of such scrap without removal of the colloiding agents is frequently unsatisfactory and this is particularly true where camphor has been used as the colloiding agent, due to the characteristic odor of camphor which is objectionable in many of the articles made from cellulose esters. Heretofore, scrap film, and the 7 like, have been treated for the removal of camphor, but many such processes result in the destruction of the cellulose ester, especially those involving treatment of the scrap with alkali and subsequent distillation of the camphor, thereby destroying the cellulose nitrate.

An object of the present invention is to provide a simple and economical process of removing colloiding agents from cellulose esters without harming either the colloiding agent or the ester. A more specific object is to provide a method of removing camphor from scrap cellulose nitrate containing camphor to obtain both the camphor and the camphor-free cellulose nitrate in satisfactory condition for reuse. Other objects will be apparent from the detailed description of the invention given hereinafter.

The above objects are accomplished according to the present invention by extracting the colloiding agent from the cellulose ester by means of an extraction medium, which is an active solvent for the colloiding agent but has merely a softening action on the cellulose ester in the presence of the colloiding agent, withdrawing the extraction medium containing the dissolved colloiding agent, and recovering the colloiding agent from 4 the extraction medium.

The extraction medium may comprise a Wide variety of solvents for the colloiding agents and may comprise a single solvent or a mixture of several solvents. The solvent selected must not have any substantial solvent effect on the cellulose ester being treated, but it'is highly advan- 'tageous that it should have sufficient solvent action on the cellulose ester in the presence of the colloiding agent to cause a softening of the cellulose ester. This softening'greatly facilitates the extraction of the colloiding agent. Ethylene dichloride, propylene dichloride, carbon tetrachloride, and chloroform are all suitable as single extraction mediums, or may be used in combination with ethyl alcohol. Ethyl alcohol is also a suitable extraction medium by itself and may be combined with benzol, toluene, water, acetone, or ethyl acetate to form a two-component solvent mixture, as well as with the chlorinated lower aliphatic hydrocarbons mentioned above. The alcoholic solvent mixture used may also be a liquid mixture of a chlorinated saturated lower aliphatic hydrocarbon containing smaller amounts of alcohol, and small amounts of benzene, toluene, water, ethyl acetate and acetone. Where a twocomponent solvent mixture is being employed, in which one component is an active solvent for the cellulose ester being treated, for example, ethyl acetate or acetone, or where one component has no substantial solvent action on the colloiding agent to be extracted, for example, water, it will be apparent that the proportions of the components of the solvent mixture can be varied at will.

From the disclosure of the extraction mediums given above, other analogous solvents, either single or two or more component mixtures, will suggest themselves to those skilled in the art. A

list of satisfactory two-component solvent mixtures suitable for use as the extracting medium is given below, showing the preferred proportion of each ingredient:

Percentages by weight Per cent Benzol 0-25 Ethyl alcohol 100-75 Toluene 0-25 Ethyl alcohol 100-75 Ethylene dichloride 100-95 Ethyl alcohol 0- 5 Propylene dichloride 100-95 Ethyl alcohol 0- 5 Water 0-10 Ethyl alcohol A 100-90 Acetone 0- 0.5 Ethyl alcohol l0099.5

Ethyl acetate." 0- 0.5 Ethyl alcohol 10099.5

suitable for carrying out the present invention,

the apparatus being illustrated more or less diagrammatically.

A preferred method of carrying out the treatment of cellulose nitrate film scrap containing camphor as the colloiding agent is as follows: The film scrap is placed in the wire basket I of the extraction kettle 2. A suitable extraction medium, for example, ethylene dichloride, is run into the kettle 2 from the storage tank 3 through the pipe 4 by opening valve 5 until the film scrap has been covered. The still 6 containing a further supply of ethylene dichloride is then heated until the boiling point of ethylene dichloride is reached, the vapors of ethylene dichloride being conducted through the pipe 1 and sparger pipe 8 into the kettle 2. This vapor raises the temperature of the ethylene dichloride in the kettle 2 to, or near, the boiling point of ethylene dichloride, which is 835 C. The temperature varies between 74-83.5 C. The heating is continued for a period of from 5-60 minutes, usually about 15 minutes, and any ethylene dichloride vaporized passes through the pipe 9 to the condenser ill and thus through pipe I I back to the storage tank 3. The level of the ethylene dichloride in the kettle 2 is kept high enough to cover the film scrap by running additional amounts of ethylene dichloride into the kettle 2 from the storage tank 3 to replace ethylene dichloride lost through volatilization. After the heating period, the ethylene dichloride in kettle 2 is run back into the still 6 through pipe l2 by opening valve I3, and then removed to recover the camphor. The cellulose nitrate film scrap is left in the basket and subjected to a second extraction treatment, if desired. Three extraction treatments are sufficient in ordinary cases to remove the last trace of camphor from the cellulose nitrate, and even a single treatment may be sufficient in some cases.

The recovery of the camphor from the ethylene dichloride is conveniently accomplished by adding water to the solution of camphor in ethylene dichloride and distilling off the ethylene dichloride. The camphor is precipitated by this step, separated from the water by centrifuging, and sublimated to obtain a pure product. The recovery of the camphor from the ethylene dichloride solution may be carried out in other ways, as will be apparent to those skilled in the art. The specific method of recovering the colloiding agent from the extraction medium forms no part of the present invention.

After the ethylene dichloride has been withdrawn from the cellulose nitrate, the cellulose nitrate may be dissolved in suitable. solvents and fillers and pigments, if present, filtered out, thereby obtaining a cellulose nitrate which has all the properties of the so-called virgin cellulose nitrate.

The proportion of extraction medium to cellulose ester to be treated may vary widely, but it has been found preferable to use from 1-15 parts by weight of extraction medium to one part by weight of cellulose ester.

The following example is given to illustrate a typical extraction of camphor from cellulose nitrate film scrap.

Example 1.-First cycle: 49.5 pounds of film scrap were placed in the extraction basket and extracted for 25 minutes with 6'75 pounds of ethylene dichloride. The extraction medium was withdrawn after this period.

Second cycle: The film scrap was then extracted for 20 minutes with 525 pounds of fresh ethylene dichloride, the extraction medium being again withdrawn after this period.

Third cycle: The film scrap was again extracted for 20 minutes with 525 pounds of fresh ethylene dichloride, the extraction medium being withdrawn after this period, and leaving a substantially camphor-free cellulose nitrate in the extraction kettle.

The approximate temperature at which the extraction steps were carried out was 74 C. The camphor was recovered from the ethylene dichloride used in the process and the extracted cellulose nitrate was dissolved and applied to a surface as a coating to see if any trace of the characteristic odor of camphor remained. It

' was found that the cellulose nitrate did not have the slightest trace of the characteristic camphor odor..

The process of the present invention is applicable to cellulose acetate and other esters of cellulose, due consideration being taken of the particular ester under treatment, in order that an extraction medium is selected having substantially nosolvent effect other than a mere softening action on the ester.

An advantage of the present invention is the recovery of the cellulose ester having essentially the properties substantially identical with socalled virgin cellulose esters, that is, cellulose ester which has not been used. The colloiding agent can be removed substantially quantitatively and recovered in pure form. The process is economical to carry out and adapted for large scale operation. Where the claims mention camphor as the colloiding agent, it is to be understood that they include obvious equivalents thereof which are soluble without change in the solvent recited.

While a particular preferred method of carrying out the invention has been described with 40 the use of ethylene dichloride as the extraction medium, it is not intended that the invention be limited to the use of ethylene dichloride as the single extraction mediums, and the two-component extraction mediums disclosed herein are all suitable for this purpose, as well as various other single and two-component extraction mediums which will be apparent to those skilled in the art from a consideration of the solvents herein disclosed.

As many apparent and widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. Process of treating. film scrap which comprises contacting said scrap with a liquid which has a solvent action on camphor and only a softening action on the cellulose derivative present, said liquid comprising essentially a chlorinated saturated lower aliphatic hydrocarbon in major proportion and smaller amounts of alcohol.

2. Process of claim 1 in which the said liquid contains a small, amount of benzol, toluene, water, ethyl acetate, and acetone.

3. The process of claim 1 which includes the steps of passing vapors of the-extraction medium through liquid extraction medium for 5-60 min utes, withdrawing the medium from the cellulosic material and recovering the extracted material.

4. In a process of recovering camphor from celluloid scrap, film base and the like, the improvement which comprises treating the celluloid material with a mixture of ethylene dichloride and ethyl alcohol. 7

5. In a process of purifying cellulose ester material, the step which comprises extracting a camphor-containing cellulose ester material with an alcoholic solvent mixture which per se is a non-solvent for the cellulose ester material but which dissolves it in the presence of camphor, and employing suflicient proportions of said alcoholic solvent mixture that it has only a softening action on the cellulose ester in the presence of the camphor.

6. In a process of purifying cellulose nitrate material, the step which comprises extracting a camphor-containing cellulose nitrate material with an alcoholic solvent mixture which per se is a non-solvent for the cellulose nitrate material but which dissolves it in the presence of camphor, and employing sufficient proportions of said alcoholic solvent mixture that it has only a softening action on the cellulose nitrate in the presence of the camphor.

7. In a process of purifying celluloid scrap, film base and the like containing camphor,- the improvement which comprises treating the camphor-contaim'ng celluloid material with an alcohol-water mixture containing at least 90% ethyl alcohol, and employing sufficient proportions of said alcoholic mixture to produce only a softening action on the cellulose nitrate in the presence of the camphor.

DORMAN MCBURNEY. EDGAR H. NOLLAU. 

